noun, plural plan·e·tar·i·ums, plan·e·tar·i·a [plan-i-tair-ee-uh] /ˌplæn ɪˈtɛər i ə/.
Examples from the Web for planetarium
The dome was lighted to represent a clear night, and, incidentally, all nights are clear in a planetarium.
Ingulfus mentions at the same time a nadir, as he calls it, or planetarium, executed in various metals.
In the school-room there was a planetarium, very neatly finished, set in motion by clock-work.Travels Through North America, v. 1-2|Berhard Saxe-Weimar Eisenach
The planets are visible during the day in the planetarium as well as night.